Inhibition of corrosive effect of halohydrocarbons



United States Patent INHIBITION OF CORROSIVE EFFECT OF HALOHYDROCARBONS George Whitlock Graham, Beloeil Station, Quebec, and George Russell Lusby, St. Hilaire Station, Quebec, Canada, assignors to Canadian Industries Limited, Montreal, Quebec, Canada, a corporation of Canada No Drawing. Filed May 13, 1959, Ser. No. 812,808 Claims priority, application Canada May 16, 1958 2 Claims. (Cl. 260-652.5)

invention relates to a method of inhibiting the corrosive effect of halohydrocarbons upon metal surfaces in contact therewith.

The marked tendency of chlorohydrocarbons, such as perchloroethylene, to undergo decomposition during storage and/or distillation, particularly in the presence of moisture, is well known. Such decomposition, when it occurs, imparts to the chlorohydrocarbons corrosive properties which render them objectionable for many purposes.

The halohydrocarbons are used extensively in commercial processes as solvents for greases and other organic matters. For example, halohydrocarbons are widely used in leather degreasing, recovery of oils and fats and in dry cleaning. They are particularly advantageous for such purposes because of their relative non-infiammability, convenient boiling points, high solvent power, and chemical inertness.

All halohydrocarbons develop a certain amount of acidity over a long period of time which renders them corrosive and thus unsuitable for some uses. In most uses for these solvents, as in dry cleaning, a charge of liquid is used over and over again. Deteriorative changes may therefore be cumulative, and are to be avoided.

The presence of certain types of soaps in dry cleaning processes also largely contributes to the corrosion of the metal parts in contact therewith.

The nature of the deteriorative changes or the chemical mechanism involved is not quite definitely known. Such changes are known to be associated with exposure to both light and air, and with the presence of moisture and acid. The presence of acidity accelerates corrosion and is quite undesirable. This is also true in dry cleaning where perchloroethylene and other similar halohydrocarbons are used extensively. Apart from damages to apparatus, any free acid contained in the solvent may be detrimental to the clothes and to some dyes.

Many different chemical bodies have been proposed for preventing the corrosive eifect of halohydrocarbons. For example, halohydrocarbons having incorporated therewith compounds such as benzaldehyde, cyclohexane, various dyes, petroleum oil fractions, toluene, etc., have been proposed as composition of matters wherein the tendency of halohydrocarbons toward decomposition and corrosiveness is suppressed. However, the use as decomposition or corrosion inhibitors of compounds such as the foregoing has been disadvantageous, principally because of the relatively large proportions of the inhibitors that must be included with the halohydrocarbons to render them effective.

It is therefore an object of this invention to provide new means whereby to inhibit the corrosive effect of halohydrocarbons.

Another object of this invention is to provide a new type of corrosion inhibitors for halohydrocarbons.

A further object of this invention is to provide a new type of corrosion inhibitors for halohydrocarbons which 2,986,586 Patented May 30, 1961 are inert to the solvent and need only be present in relatively small concentrations.

A still further object of this invention is to provide noncorrosive halohydrocarbons as solvents for greases and other organic matters.

Other objects of this invention will become apparent hereinafter.

Broadly speaking, this invention provides a method of inhibiting the corrosive eifect of halohydrocarbons upon metal surfaces in contact therewith by incorporating with said halohydrocarbons, essentially, a small proportion of a metal salt of a weak organic acid, the metal being selected from the group consisting of lead and metals of groups 1(a) and II of the periodic table, said salt being non-corrosive to the metal parts in contact therewith.

The preferred salts other than those of lead which may be used in connection with the present invention are the salts of sodium, potassium, calcium, barium, strontium, magnesium and zinc salts of naphthenic, stearic, palmitic and oleic acids.

The concentration of these soluble salts in the halohydrocarbons may vary within Wide limits depending on the metal in contact therewith and the halohydrocarbons themselves. For example, a concentration of (Ll-2.0% by weight of calcium stearate in perchloroethylene has shown sucessful results.

The following example will now illustrate the preferred embodiments of the invention, but in no way is it intended to limit the scope thereof.

EXAMPLE I Diiferent tests of corrosiveness were conducted in an apparatus consisting of a 500 ml. conical flask, a reflux condenser, and a water trap located between the condenser and the flask. The trap was constructed in such a way that vapours from the flask passed through a large glass tube into the condenser, while the condensate flowed down into a small side tube containing a layer of 3 ml. of water. After passing through the water, the perchloroethylene overflowed continuously into the boiling flask. In this way the volatile corrosive compounds from a 200 ml. sample of boiling perchloroethylene were concentrated in 3 ml. of water, and the rate of corrosion was thus greatly accelerated.

In order to obtain a measurable amount of corrosion, a stainless steel strip was placed in a vertical position in the perchloroethylene-Water trap so that it projected up into the condenser, and tests were carried out for 5 days, at the end of which the corrosion was measured by the loss in weight of the metal strip.

In order to obtain conclusive results, the aforesaid tests were also conducted in the presence of a commercial still residue which consisted of material left in the still pot of a dry-cleaning plant, after the perchloroethylene had been distilled oif.

Still residues usually contain soaps and other soluble matter and some suspended matter which accumulate in the perchloroethylene during the cleaning of clothing. Their compositions are quite complex and little is known, except that they appear to contain some acidic constitucuts.

The compositions of still residues naturally vary from one dry-cleaning plant to another, depending on the nature of the process and the type of clothing being cleaned. Samples of still residues were obtained from different plants and the above residue was found to have the most corrosive effect on stainless steel in the above tests.

The results obtained and the different conditions under which the experiments took place are summarized in the following table. In these tests the corrosion inhibitor 3 was introduced in the flask in admixture with the perchloroethylene and 1.6% by weight of the above still residue.

Table l AFTER 5-DAY TEST Corrosion inhibitors Loss in wt.

of metal strip, gr.

Percent wt.

OOU'H- What we claim is:

1. A method of inhibiting the corrosive efieet of perchloroethy-lene upon metal surfaces in contact therewith which comprises, essentially, incorporating with said perchloroethylene from 0.1% to 2.0% by weight of a metal salt selected from the group consisting of calcium stearate, magnesium stearate, calcium palmitate, lead naphthenate and basic lead stea-rate.

2. A non-corrosive composition of matter comprising, essentially, perchloroethylene and from 0.1% to 2.0% by weight of a metal salt selected from the group consisting of calcium stearate, magnesium stearate, calcium palmitate, lead naphthenate and basic lead stearate.

References Cited in the file of this patent UNITED STATES PATENTS 2,671,064 Cowell et al. Mar. 2, 1954 2,781,406 Dial Feb. 12, 1957 2,906,783 Monroe et al Sept. 29, 1959 FOREIGN PATENTS 545,500 Great Britain May 29, 1942 OTHER REFERENCES Neuville et al.: 1st addition to French Patent 649,934, dated Sept. 10, 1928, addition Patent No. 35,060, June 18, 1929. 

1. A METHOD OF INHIBITING THE CORROSIVE EFFECT OF PERCHLOROETHYLENE UPON METAL SURFACES IN CONTACT THEREWITH WHICH COMPRISES, ESSENTIALLY, INCORPORATING WITH SAID PERCHLOROETHYLENE FROM 0.1% TO 2.0% BY WEIGHT OF A METAL SALT SELECTED FROM THE GROUP CONSISTING OF CALCIUM STEARATE, MAGNESIUM STEARATE, CALCIUM PALMITATE, LEAD NAPHTHENATE AND BASIC LEAD STEARATE. 